Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$80.51	8.483%	$87.3397	$87.34	$87.35	$87.30
Purchase #2	$68.41	6.814%	$73.0715	$73.07	$73.05	$73.10
Purchase #3	$50.33	9.162%	$54.9412	$54.94	$54.95	$54.90
Purchase #4	$98.38	7.221%	$105.484	$105.48	$105.50	$105.50
Purchase #5	$90.28	11.512%	$100.673	$100.67	$100.65	$100.70
Purchase #6	$119.31	7.757%	$128.5649	$128.56	$128.55	$128.60
Purchase #7	$48.81	5.509%	$51.4989	$51.50	$51.50	$51.50
7 purchase totals =	$556.03		$601.5732	$601.56	$601.55	$601.60